A piston reciprocating in a cylinder creates a great deal of friction between the outer surface of the piston and the adjacent cylinder wall of an internal combustion engine. Oil is used to lubricate the contacting surface between the piston and the cylinder wall. The oil used to lubricate tends to move up the cylinder wall, providing a smooth lubrication surface across which the piston may traverse. However, if the oil is allowed to move up the piston wall unrestrained, excess oil flows into the combustion chamber of the cylinder where it is ignited. Unrestrained oil flow not only wastes oil, but it causes the internal combustion engine to emit excess noxious gas. Consequently, at least one oil control ring is placed in an outer annular groove on the piston to scrape oil away from the combustion chamber. When gas that has been drawn into the combustion chamber is ignited and explodes, the piston is pushed away from the chamber by the force of the explosion. The oil control ring contacts the cylinder wall and scrapes oil away from the combustion chamber.
However, the oil control ring may not be able to quickly or effectively contact the cylinder wall due to pressure from blow-by gases that are created by the explosion in the combustion chamber. Blow-by gases tend to move out of the combustion chamber and down the cylinder wall. The pressure produced by the blow-by gases pushes the oil control ring away from the cylinder wall. Consequently, oil is not properly scraped away from the combustion chamber.
Pistons have been designed with openings used to either drain oil or to relieve blow-by gas pressure. However, holes used to vent blow-by gas are typically susceptible to a problem called reverse oil pumping where oil flows from the interior of the pistons through blow-by relief openings to the cylinder walls which actually allows more oil to get to the combustion chamber.
The present invention seeks to provide relief from blow-by gas pressure to allow an oil control ring to more effectively scrape a cylinder wall while avoiding the problem of reverse oil pumping.